This programme of work was initiated as a result of recent major changes within Europe that have impacted upon the type of masonry mortars that are in use and the appropriate test procedures. A new suite oftest method standards, the EN 1015 series, has been issued by CEN over the last few years and supports two new mortar standards, BS EN 998-1 and BS EN 998-2, which are for plastering and rendering and masonry mortars respectively. In addition, there has been a large increase in the use of factory made mortar. Factory production, particularly as a dry mortar, leads itself to the production of more complex mortar formulations, and some mortars now contain as many as eight separate admixtures. These changes have lead to a large increase in the number of mortars that are highly air entrained, whilst the use of retarders and other admixtures in these mortars means that they frequently have pronounced thixotropic and other time dependant properties. All of these changes have in turn led to greater complexity in the fields of test methods and procedures. This thesis describes an investigation to define the properties of plastic mortar from first principles, then to compare these properties with the results produced by existing test methods to confirm ifthe latter were adequate. It was found that there were some properties for which several test methods existed, but some for which there were none. A test programme was then developed to investigate in detail and then to compare some relevant test methods, including new European ones and the older British ones that they replaced. Finally, two new, procedures were developed, one based on rheometry, one on the measurement of the early heat of hydration. Recommendations are made that these test procedures be further developed with a view to their adoption as standard tests.